The mechanisms that are responsible for modulating sympathetic outflow in the normal state have been investigated for many years and are widely accepted as those which involve peripheral reflex feedback as well as hormonal mediation of neurotransmission in classical pressor and depressor areas of the medulla. The situation in sympatho-excitatory states is not as clear. Our previous studies along with the preliminary data described in this grant application indicate that important components in the generation of sympatho-excitation in chronic heart failure (CHF) are the substances angiotensin II (Ang II) and nitric oxide (NO). While these substances may have direct effects on central synaptic function they also may act indirectly by activation of additional pathways. Our preliminary data suggest that reactive oxidant species (ROS) are important contributors to the sympatho-excitatory state in CHF. In this proposal we hypothesize that many of the central sympatho-excitatory actions of Ang II in the CHF state are mediated by activation of the pro-oxidant enzyme NAD(P)H oxidase. We propose experiments using novel methodological tools to understand the role of ROS and NAD(P)H oxidase in sympatho-excitation at rest and in response to Ang II in rabbits with CHF, evaluate the interaction between NO and Ang II in the central nervous system of rabbits with CHF, determine the effects of exercise training on the sympatho-excitatory responses to Ang II and on the involvement of NAD(P)H oxidase in these responses. In order to carry out these experiments we will use both pharmacological and genetic manipulations of superoxide dismutase and NAD(P)H oxidase. We will determine the role of the Ang II type 1 receptor in mediating these responses and its role in chronic changes of ROS in the CHF state. Overall, these studies will provide new information on the role of ROS in the sympatho-excitation and pathogenesis of CHF. Interventions that are likely to reduce the influence of central ROS will be another important outcome of these experiments. Finally, this project is highly interactive with the other 3 projects in this PPG.